While I don't think we have ever used this feature in any of our classes, it is not evident to me why activities and manually entered items would be treated differently.
My understanding is that "offset", for example, would be used by an instructor who decides to add a few points to a test after she determines that a certain question is ambiguous. But this is just as likely to happen if the item was done offline as online. The same might go for multiplier if the teacher is using it as a method of scaling.
Looking at the original bug, I also don't understand why this scaling or transformation would not apply to overridden grades based on my perception of why this feature is made available.
As this may cause confusion, it might be helpful to discuss why it is available to only non-overridden activities.